Exemplary applications for this invention include space-based radar systems, situational awareness radars, and weather radars. Space based radar systems will use electronically scan antennas (ESAs) including hundreds of thousands of radiating elements. For each radiating element, there is a phase shifter, e.g. 3 to 5 bits, that, collectively in an array, control the direction of the antenna beam and its sidelobe properties. For ESAs using hundreds of thousands of phase shifters, these circuits must be low cost, be extremely light weight (including package and installation), consume little if no DC power and have low RF losses (say, less than 1 dB). For space sensor applications (radar and communications) these requirements exceed what is provided by known state of the art devices.
Current state of the art devices used for RF phase shifter applications include ferrites, PIN diodes and FET switch devices. These devices are relatively heavy, consume relatively large amounts of DC power and are relatively expensive. The implementation of PIN diodes and FET switches into RF phase shifter circuits is further complicated by the need of additional DC bias circuitry along the RF path. The DC biasing circuit needed by PIN diodes and FET switches limits the phase shifter frequency performance and increase RF losses.
A switched loop RF radiator circuit is disclosed, comprising a radiator element, a circuit RF input/output (I/O) port, and a balun coupled between the radiator element and the I/O port. The balun includes a 180xc2x0 switched loop circuit having two transmission line legs coupled to a balun transition to provide a selectable 180xc2x0 phase shift, and a microelectromechanically machined (MEM) switch circuit to select one of the transmission line legs.
Many radiator circuits can be deployed in an electronically scanned antenna array.